The present invention relates to an apparatus for the treatment of sewage effluent and particularly such apparatus comprising a rotating biological contactor. Various types of rotating biological contactor are known for example that described in my earlier European Patent Specification No. 0 249 433.
Hitherto, rotating biological contactors have been constructed in very many different ways but essentially comprise an open rotor structure of semi-buoyant lightweight material which is rotatable on a shaft and which is partly submerged in the effluent to be treated. The rotor includes or defines a structure having a high surface area providing a suitable substrate for biomass growth, such as a series of discs which may be embossed (e.g. GB 2,118,535A), or divided into sectors (e.g. GB 1,394,552), a drum defined by an open mesh enclosing loose particulate media (e.g. GB 1,408,235), or sheets or tubes wound in a spiral or helical fashion about the shaft (e.g. GB 1,509,712, EP 0,198,451A). It has also been proposed (e.g. WO 81/00101) to use a spiral or helical rotor structure to provide nett lift to the effluent during rotation in the manner of an Archimedes Screw.
Danish Patent Application 2002/83 discloses a drum structure having two sets of spiral vanes wound in opposite directions and divided by a single axially mounted disc which defines a partition. The inlets and outlets are located at opposite ends of the drum near the shaft and not at the periphery of the drum end faces. A lifting and lowering effect is obtained by the oppositely wound spiral vanes in this arrangement to pass effluent through the contactor. A certain minimum quantity of effluent is present in the drum at any given time to make the drum more buoyant and so reduce the load on the shaft.
Danish Patent Application 0089/84 discloses a non-partitioned drum having a spiral vane construction which has inlets near the periphery of the drum.
DE 3 409 111 A describes a contactor having a series of discs which sandwich between them spiral vanes but wherein no enclosing shell or drum structure is provided. It is necessary to almost submerge the contactor in this instance which increases the load on the shaft.
U.S. Pat. No. 4,160,736 describes a drum structure having closely spaced discs mounted on a shaft with a spiral vane arrangement at each end of the drum having the function of carrying effluent towards inlets and outlets which are located in the axial region at the respective end faces of the drum. A relatively small quantity of effluent is held in the drum at any given time which acts as a "rotating trickling filter" and does not provide the same positive aeration by virtue of churning action as provided by a contactor having an enclosed spiral vane arrangement.
It is also known to utilize a rotating biological contactor in conjunction with one or more independent settlement tanks.
It is an object of the present invention to provide an apparatus which can effect the efficient treatment of raw sewage effluent so as to render it safe for discharge by spreading on land or by introduction into natural waterways.
It is another object of the invention to provide compact apparatus including a rotating biological contactor for removing substantially all particulate or solids material from sewage effluent without the necessity for separate "in-line" settlement tanks, which take up considerable space.
It is a further object of the invention to provide sufficient aeration of effluent combined with maximum contact with biological agents in order to reduce the biological oxygen demand (BOD) of the effluent to a safe level.